1. Technical Field
The invention relates to the installation of elevators in general, and to an apparatus and a method for balancing elevator cars in particular.
2. Background Information
A typical elevator system comprises an elevator car and a counterweight driven within a hoistway by a drive sheave. A plurality of hoist ropes connect the car and the counterweight, extending up from the car to the drive sheave at the top of the hoistway, and back down to the counterweight. When the car and counterweight are at the opposite ends of the hoistway, and the hoist ropes are therefore almost entirely on one side, the hoist ropes comprise a significant percentage of the weight drawn by the drive sheave. To offset the weight of the hoist ropes, it is known to use one or more compensating ropes extending from the car down the hoistway and back up to the counterweight. Compensating "ropes" may actually be cables or chains, depending on the application. Chains are often used in short run elevators.
A traveling cable may also be attached to the car. Traveling cables include a plurality of power and communications lines combined in to a single bundle extending between a fixed position in the hoistway and the car. Both the compensating ropes and the traveling cable are attached to the frame of the car in fixed positions after installation.
During installation of the elevator, the elevator car must be balanced to ensure proper operation of the elevator and to optimize the elevator ride. Correctly positioning and attaching the compensating ropes and the traveling cable relative to the car is an important part of the balancing process. One method for balancing the elevator car involves a weight assembly attached to the car isolation frame by a plurality of conventional fasteners. Each weight is positioned along the isolation frame member and set in place using a plate, a plurality of bolts and spring washers. The mechanic positions the weight where he or she believes it is necessary, fastens it to the frame member using the plates, bolts, and washers, and subsequently checks for balance.
A disadvantage of this balancing system is that the weights are cumbersome to attach to the frame member underneath the car. Specifically, the mechanic must either hold or prop each weight in place and at the same time position the plates and thread the fasteners for each weight. Another disadvantage of this system is that all the weights must be fixed in place before the car can be checked for balance. If the balance is not correct the first time, the weights must be unbolted (or the bolts must at least be loosened) and repositioned. Practically speaking, the weights are bolted, unbolted, moved, and rebolted several times during the process. A person of skill in the art will recognize that this is a time consuming job that often leads to inaccuracies.